1. Field of the Invention
This invention relates to a process for recovering petroleum from subterranean formations by aqueous surfactant flooding using a dicyclopentadiene derived ethoxysulfonate containing fluid. In another embodiment, the invention relates to a petroleum recovery fluid comprising petroleum sulfonates and a solubilizing amount of a dicyclopentadiene derived ethoxysulfonate in aqueous medium.
2. Description of the Prior Art
Crude oil which has accumulated in subterranean is recovered or produced through one or more wells drilled into the reservoir. In the initial production, the crude oil is produced by primary recovery techniques wherein only the natural forces present in the reservoir are utilized to produce the oil. However, upon depletion of these natural forces and the termination of primary recovery a large portion of the crude oil remains trapped within the reservoir. Additionally, many reservoirs lack sufficient natural forces to be produced by primary methods from the very beginning. Recognition of these facts has led to the development and use of many enhanced oil recovery techniques. Most of these techniques involve injection of at least one fluid into the reservoir to produce an additional amount of crude oil. Some of the more common methods are water flooding, steam flooding, CO.sub.2 flooding, polymer flooding, surfactant flooding, caustic flooding, and in situ combustion.
Water flooding, which involves injection of water into the subterranean oil reservoir for the purpose of displacing the crude oil from the pore spaces of the reservoir rock toward the producing wells, is the most economical and widely used of the enhanced oil recovery methods. Nevertheless, water does not displace oil with high efficiency because of the immiscibility of water and oil and because of the high interfacial tension between them.
Surfactant flooding involves the addition of one or more surface active agents or surfactants to the water flood for the purpose of minimizing the water flooding problems mentioned above. This has been an area of active interest in the art of enhanced oil recovery methods for many years. U. S. Pat. No. 3,302,713 discloses the use of petroleum sulfonates as effective surfactants in oil recovery operations. Other surfactants proposed for use in oil recovery processes include alkyl sulfates, alkyl aryl sulfates, alkyl or alkyl aryl ethoxy sulfates, alkyl sulfonates, alkyl aryl sulfonates, and quaternary ammonium salts.
While the above surfactants may be effective under ideal conditions, there are problems concerned with the use of each in most petroleum reservoirs. Some of the most serious problems arise from the effects of reservoir fluid salinity on the injected surfactant solution, the most common being precipitation and resultant loss of the surfactant. The petroleum sulfonates represent a class of surfactants that are relatively inexpensive and that are quite effective oil recovery agents under certain conditions. However, when used in single surfactant systems, they are best employed in reservoirs having brines of 10,000 ppm or less total dissolved solids salinity and a very low divalent ion concentration. Effectiveness of a petroleum sulfonate surfactant system can be extended somewhat by blending oil soluble petroleum sulfonates with water soluble petroleum sulfonates. However, even a solution such as this is not entirely satisfactory because as the blended mixture is driven through the formation one of the components is often preferentially retained within the formation matrices, causing a change in the relative concentration of the surfactant components and resulting in a failure to maintain effective salinity tolerance as evidenced by precipitation of the sufactants.
It can readily be seen that there remains a substantial need for a surfactant flooding process that will allow the use of petroleum sulfonates in high salinity and high divalent ion concentration reservoir environments.
U.S. Pat. No. 4,140,724, Nyi et. al., describes reactions involving dicyclopentadiene.